i16018b.scala

// Regression test for #16018: the akka-derived shapes.
//
// These exercise the path that motivated the original ticket: a value of
// type `J[? <: G[? <: M]]` (J a Java generic) flows through a method that
// re-projects it as a Scala collection, and is then `collect`/`map`-ed with
// a subtype pattern + a fallback `case other`. The combination triggers
//   (i)  `Inferencing.captureWildcards` — the Java-generic argument becomes
//        a TypeBox.CAP skolem `?N.CAP`, and
//   (ii) `Match` typing — pattern narrowing turns the first case body into
//        `pat ∩ ?N.CAP`, while `case other` keeps the raw `?N.CAP`.
//
// Until the fix in `TypeComparer.compareCaptured` for wildcard-bound
// existential widening, the inferred result type could not escape the
// skolem cleanly. See:
//   - tests/pos/i16018.scala — companion pos matrix (pure-Scala)
//   - scala/scala3 #16018 — original bug report

object Test:

  class Container[+S, +M]
  class SubContainer[+S, +M] extends Container[S, M]

  def seqOf[T](it: java.lang.Iterable[T]): scala.collection.immutable.Seq[T] = ???

  // ---- f1: trigger via java.lang.Iterable ----------------------------
  def f1[M](xs: java.lang.Iterable[? <: Container[Any, ? <: M]])
      : scala.collection.immutable.Seq[Container[Any, M]] =
    seqOf(xs).collect {
      case g: SubContainer[Any, M] @unchecked => g
      case other                              => other
    }

  // ---- f2: same trigger via java.util.List ---------------------------
  def f2[M](xs: java.util.List[? <: Container[Any, ? <: M]])
      : scala.collection.immutable.Seq[Container[Any, M]] =
    seqOf(xs).collect {
      case g: SubContainer[Any, M] @unchecked => g
      case other                              => other
    }

  // ---- f3: same trigger via .map instead of .collect -----------------
  def f3[M](xs: java.lang.Iterable[? <: Container[Any, ? <: M]])
      : scala.collection.immutable.Seq[Container[Any, M]] =
    seqOf(xs).map {
      case g: SubContainer[Any, M] @unchecked => g
      case other                              => other
    }